In the past, radiofrequency (RF) generators and electrodes have been applied near or in neural tissue, for relieving pain or modifying its function. By way of one example, a lesion generator identified by Model No. RFG-3C RF, available from a company named Radionics, Inc., located in Burlington, Mass., has electrodes, which may be placed near a desired neural tissue area. The desired neural tissue area is heated by radiofrequency (RF) resistive power dissipation of the generator power deposited in the tissue. In some cases, thermal monitoring by a thermo sensor in the electrode is used to control the process. It is common to form heat lesions with tissue temperatures ranging from 60 to 95 degrees Celcius (.degree. C.). Tissue generally dies when heated to about 45.degree. C. to 50.degree. C., which causes the patient to suffer severe, if not, unbearable pain. The pain levels are so intense, that local or general anesthetic is often required during such a procedure. Use of local or general anesthetic exposes a patient to undesired risks, and the destructive nature of and unpleasant side effects of the radiofrequency (RF) heat lesions are limitations of this technique, which is well known. Heat lesion generators typically use continuous wave radiofrequency (RF) generators with radiofrequency ranges from 100 Kilo Hertz to several Mega Hertz. Heat lesion generators are available from several companies such as Radionics, Fisher, OWL, Elekta, Medtronic, Osypka, EPT, and so on. The theoretical aspects and use of RF lesion generators and electrodes for relieving pain and functional disorders is discussed in various papers, two of which are: (1) Cosman, et al., "Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone," Neurosurgery 15:945-950, 1984; and (2) Cosman E R and Cosman B J, "Methods of Making Nervous System Lesions," in Wilkins R H, Rengachary SS (eds): Neurosurgery, New York, McGraw-Hill, Vol. III, 2490-2498, 1984.
Neural stimulation has also recently become a common method for pain therapy. For neural stimulation, stimulus generators are generally used, which typically have output levels between 0 to 10 volts (or zero to several milliamperes of current criteria are used). A variety of waveforms and pulse trains in the "physiologic" frequency ranges of 0 to about 300 Hertz are also typically used. This output is delivered to electrodes placed near to in neural tissue on a temporary basis (acute electrode placement) of permanent basis (chronic electrode implants). Such stimulation can relieve pain, modify neural function, and treat movement disorders. Typically, in most cases the stimulation must be sustained to have long-term effects. That is, usually when the stimulus is turned off, the pain returns or the therapeutic neural modification ceases after a short time (hours or days).
Thus, it is standard practice to use permanent implant electrodes and stimulators, which may be operated on battery power or induction driven. An example of such a commercially available system is one manufactured by Medtronic, Inc., located in Minneapolis, Minn. With permanent implant electrodes and stimulators, the stimulus is usually sustained or repeated on an essentially continuous basis for years, to suppress pain or to treat movement disorders, for example, Parkinsonism, bladder control, spasticity, etc. Stimulators deliver regular pulse trains or repetitive bursts of pulses in a range between 0 to 200 Hertz, which corresponds to a human body's physiological range of neural frequency pulse rates. This method stimulates or inhibits neural function. It does not seek to heat the neural tissue for destructive purposes as in high frequency technique.
Chronologically or permanently implanted stimulators of the type discussed above, require frequent battery changes or long-term maintenance and patient follow-up, which is expensive and inconvenient, often requiring repeated surgery.
Electrosurgical generators have commonly been used in the past for cutting and coagulating tissue in surgery. They typically comprise a high frequency, high power generator, which is connected to an electrode that delivers its high power output to explode tissue for purposes of cutting, cooking, searing, or otherwise coagulating tissue to stop bleeding. Examples of such systems are generators available from a company named Codman, Inc., located in Randolph, Mass., or from a company named Valley Labs, Inc., located in Boulder, Colo., or from a company named EMC Industries, located in Montrouge, France. Such generators have high frequency output waveforms, which are either continuous waves or interrupted or modulated waves. Such generators have high power levels and duty cycles, which when applied to the electrode, shatter and macroscopically separate tissue (in a cutting mode) or heat the tissue to very high temperatures, often above cell boiling (100.degree. C.) and charring levels (in a coagulation or cauterizing mode). It should be recognized that the purpose of electrosurgery generators is surgical, not therapeutic. Thus, their output controls, power ranges, duty cycles, waveforms, and monitoring capabilities are not designed for gentle, therapeutic, neuro-modulating, sub-lethal temperature applications. Use of an electrosurgical unit requires local or general anesthetic because of its violent effect on tissues, whose temperature levels are raised to very high levels.